The Ulnar Forearm Fasciocutaneous Flap

The ulnar forearm fasciocutaneous flap is a perforator flap that is anatomically similar to the radial artery forearm flap. A thorough anatomic understanding of the vascular supply of the hand and a good clinical exam are necessary for appropriate flap selection. The ulnar and radial arteries are the two main arteries that provide blood supply to the hand, with the ulnar being the larger of the two. Distally, the two arteries merge to form two palmar arches: one deep and one superficial. When the arches are intact, vascular perfusion can often be maintained with the existence of one artery or the other. The superficial palmar arch is mainly formed by the ulnar arch with the aid of a smaller superficial branch of the radial artery. The superficial palmar branch is incomplete in 1/5 of the patients and supplies typically the little, ring, long finger, and the ulnar aspect of the index finger. The deep palmar arch on the other hand is formed mainly by the radial artery with the aid of the deep palmar branch of the ulnar artery. Contrary to the superficial palmar arch, it is almost always complete and provides blood supply to the thumb and the radial aspect of the index finger. A preoperative Allen’s test can help define radial or ulnar dominance of the hand with regards to the vascular supply, as well as the presence of complete palmar arches. Since the superficial palmar branch is more likely to be incomplete, sacrifice of the radial artery may lead to ischemic changes in the hand more often than sacrifice of the ulnar artery. If that is the case, a radial forearm flap should not be harvested and an ulnar forearm flap should be considered. On the rare occasion where the distal blood supply of the radial and ulnar arteries is completely independent, the use of either the radial or ulnar forearm flap cannot be justified. It needs to be noted that due to a paucity of ulnar cutaneous perforators distally in the forearm, the ulnar forearm flap cannot be designed as distal as the radial forearm flap. Of note, the ulnar pedicle is shorter than the pedicle of the radial forearm flap. However, the skin overlying the ulnar aspect of the forearm is usually thinner and less hair bearing compared to the radial aspect and may result in a more cosmetically acceptable result for some patients. The donor site defect is also more easily concealed. However, the ulnar forearm flap is associated with significant post - operative morbidity, since it is harvested from an area of the forearm that is used to rest the upper extremities during daily activities (for example when using a keyboard or when writing). Finally, similar to the radial forearm flap, the ulnar forearm flap can be raised as chimeric flap with the ulna, and or flexor carpi ulnaris. It can also be used as a flow-through flap if distal revascularization is desired.